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| United States Patent |
6,048,595
|
|
Nakajima
, et al.
|
April 11, 2000
|
Printed articiles having light-storing printed layers
Abstract
The present invention provides a superior light-storing printed article,
which includes a light-storing printed layer comprising 50-80 wt % of
light-storing pigment having D50=22-35 .mu.m and D90=58-80 .mu.m based on
the total amount of the light-storing pigment and the binder, and the
thickness of the printed layer being 50-150 .mu.m.
| Inventors:
|
Nakajima; Hiroyuki (Saku, JP);
Tanaka; Kimio (Komoro, JP);
Higashi; Shuji (Saku, JP);
Fujii; Tatsuo (Saku, JP)
|
| Assignee:
|
TDK Corporation (Tokyo, JP)
|
| Appl. No.:
|
859989 |
| Filed:
|
May 21, 1997 |
Foreign Application Priority Data
| Sep 18, 1996[JP] | 8-266605 |
| Feb 05, 1997[JP] | 9-035674 |
| Current U.S. Class: |
428/40.1; 40/542; 40/543; 242/344; 242/347; 360/132; 428/40.2; 428/41.6; 428/42.1; 428/203; 428/204; 428/207; 428/913 |
| Intern'l Class: |
B32B 027/20 |
| Field of Search: |
428/40.1,40.2,41.6,41.7,41.8,42.1,203,204,207,913
250/484.4
40/542,543
242/344,347
360/132
|
References Cited
U.S. Patent Documents
| 5698301 | Dec., 1997 | Yonetani | 428/213.
|
| 5725169 | Mar., 1998 | Odagiri | 242/344.
|
| Foreign Patent Documents |
| 700046A2 | Mar., 1996 | EP.
| |
| 59-142981 | Sep., 1984 | JP.
| |
| 62-80282 | May., 1987 | JP.
| |
| 5-36229 | Feb., 1993 | JP.
| |
| 8-230967 | Sep., 1996 | JP.
| |
Primary Examiner: Ahmad; Nasser
Attorney, Agent or Firm: Wood, Phillips, VanSanten, Clark & Mortimer
Claims
What we claimed is:
1. A printed article including an article and a light-storing printed layer
on the front side of said article, said light-storing printed layer
containing 50-80 wt % of light-storing pigment and a balance binder, said
pigment having D50=22-35 .mu.m and D90=58-80 .mu.m, and the thickness of
the printed layer being 50-150 .mu.m.
2. A printed article including an article and a light-storing printed layer
on the front side of said article according to claim 1, wherein said
printed article further includes a writable printed layer of a transparent
or translucent material which provides a receptive surface for writing,
formed on the light-storing printed layer.
3. A printed article including an article and a light-storing printed layer
on the front side of said article according to claim 1, wherein said
printed article further includes a light reflective layer on the rear side
of the light-storing printed layer.
4. A printed article including an article and a light-storing printed
article on the front side of said article according to claim 2, wherein
said printed article further includes a light reflective layer on the rear
side of the light-storing printed article.
5. A printed article including an article and a light-storing printed layer
on the article according to claim 2, or 4, wherein said printed article is
a label sheet to be affixed to an object, said label sheet having an
adhesive layer and release paper on the rear side of a label sheet
substrate and also having said light-storing printed layer formed closer
to the front side of the substrate than the adhesive layer, the writable
printed layer is formed closer to the front side than the light-storing
printed layer, said writable printed layer enabling the user to see at
least a part of said light-storing printed layer through said writable
printed layer.
6. A printed article including an article and a light-storing printed
article on the article according to claim 2, or 4, wherein said printed
article is a label sheet having an adhesive layer and release paper on the
rear side of said label sheet substrate which consists of a paper or film
sheet and also having said light-storing layer on the front side of the
substrate, said writable printed layer printed with a transparent or
translucent writable ink formed on at least a part of the light-storing
printed layer.
7. A printed article including an article and a light-storing printed
article on the article according to claim 2, or 4, wherein said printed
article is a label sheet having said light-storing printed layer on a
label sheet substrate which consists of a transparent or translucent film
sheet and also having an adhesive layer and release paper on the rear side
of the substrate, the light-storing printed layer is provided on the rear
side of the label sheet substrate, the adhesive layer is so provided as to
cover at least a part of the light-storing printed layer, and a writable
printed layer printed with a transparent or translucent writable ink is
formed on at least a part of the front side of the label substrate.
8. A printed article including an article and a light-storing printed
article on the article according to claim 2, or 4, wherein said writable
printed layer is a printed layer from an ink containing a binder and one
of the powders of the group consisting of protein, silica and wooden
cellulose powders.
9. A printed article according to claim 1 including an article and a
light-storing printed article on the article, wherein said article
comprises a first label sheet and a second label sheet in combination,
said first label sheet consisting of a label sheet substrate which
consists of a paper or film sheet, said light-storing layer printed on the
front side of the substrate, an adhesive layer on the rear side of said
substrate and a release sheet formed on the rear side of the adhesive
layer, said second label sheet consisting of a transparent or translucent
film sheet substrate, a printed writable layer printed on the front side
of said film sheet substrate with an ink which permits writing, and an
adhesive layer on the rear side of said film sheet substrate which is
attached to the surface of said light-storing layer.
10. A printed article including an article and a light-storing printed
article on the article according to claim 3, wherein said article is a
tape cassette, said light reflective layer is formed on an area of said
cassette which can be seen from outside, and said light-storing printed
layer is formed on said light reflective layer.
11. A printed article according to claim 10, wherein a writable printed
layer is formed on said light-storing printed layer.
12. A printed article according to claim 10, wherein said article is a tape
cassette comprising a case and a liner sheet within said case inserted
between a wound tape and and an inner wall of said case, said reflective
layer is formed on the liner sheet in an area which can be seen through a
transparent portion of said case, and said light-storing printed layer is
formed on said reflective layer.
13. A printed article according to claim 10, wherein said area which can be
seen from outside is in an area on the outer surface of said cassette, and
said light reflective layer and said light-storing layer are formed
directly on said area.
14. A printed article according to claim 10, wherein said area which can be
seen from outside is in an area on the outer surface of said cassette, and
said light reflective layer and said light-storing layer are formed on
said area, said reflective layer being provided with an adhesive layer on
the rear side on a release sheet which has been peeled.
15. A printed article according to claim 12, wherein a writable label which
is transparent or translucent is attached to a portion of said case
through which said light-storing layer can be seen.
Description
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
This invention relates to printed articles having light-storing printed
layers and label sheets having such light-storing printed layers for use
in indicating information and the like on audio and video tape cassettes
and other recording media such as MDs, MFDs, and CDs, or on cases of paper
or plastics holding those media for storage. The invention also relates to
articles provided with such light-storing printed layers.
2. Prior Art
Audio and video tape cassettes, MDs, and other disc cassettes are furnished
with label sheets which the user can affix, after inscription of
appropriate information or the like, to the casings or housings of the
cassettes themselves or to the cases containing the cassettes. These
housings and cases usually have receptive areas for labeling, each
consisting of a recess to which a label can be attached. The user writes
information on the label with a pencil, ballpoint pen, or other writing
implement, and then sticks it on each cassette housing or each case for
the housing, or vice versa. Each label has a blank space to be filled out
with a subject of the contents, title of music, or other information,
besides identification marks and other inscription that facilitate the
user's choice according to the intended use.
FIG. 1 is a perspective view of a conventional audio tape cassette, showing
a label 2 affixed to the cassette housing 1, with a blank surface 5 to be
filled out. FIG. 5 is a cross sectional view indicating a typical
structure of prior art label sheet 2. A writable label base 3 is lined
with an adhesive layer 7, which in turn is protected on the opposite side
with release paper 9. Before use, the release paper 9 is peeled off, and
the label base 3 with the adhesive layer 7 is attached to the cassette
housing 1 in the correct position.
The ink commonly used in printing writable label sheets is an offset or
silk screen printing ink of ordinary composition for identification of
sides A and B and for decorative designing of cassette housings 1. The
ordinarily printed labels are identifiable and legible in the sunlight or
illumination, but not in the dark. As an additional user-oriented feature,
there is a growing demand for labels as useful at night, particularly in
the dark, as in the light.
Some approaches have been made to meet the demand. One approach, as
typically proposed by Japanese Utility Model Application Kokai No.
62-80282, uses a light-storing, phosphorescent paint in giving
identification and indication directly to the both sides A and B of
cassette housings so that the user can clearly differentiate between the
two sides in a dark place.
Another approach, as according to Utility Model Application Kokai No.
59-142981, offers a label consisting of a label base, a self-emitting,
luminous paint layer formed on the base surface, and a scratchable layer
formed further on it by opaque printing.
Further, EP0700046A2 (Japanese Patent Application Kokai No. 8-77746)
proposes to apply a light-storing printed layer having a light-storing
property over about eight hours in which calcium carbonate or protein
powder is mixed on a label sheet to be attached to a cassette, or directly
on a cassette using a screen printing method, in order to impart both the
light-storing property as well as the writing property to the
light-storing layer on which letters or symbols may be directly written
with a writing instrument like a pencil.
A few more techniques have been introduced to help distinguish letters and
alphanumerical symbols on part of cassette housings, such as of magnetic
tape cassettes, by printing them in white ink or light-storing ink.
For example, Japanese Patent Application Kokai No. 63-117383 came up with a
liner sheet base containing a light-storing pigment so that the tape
condition inside the cassette can be observed in the darkness.
Problems to be Solved
The use of phosphorescent paint in direct inscription as proposed by
Utility Model Application Kokai No. 62-80282 does not allow the user to
write necessary information on the cassette.
The label according to Utility Model Application Kokai No. 59-142981 that
comprises a self-emitting, luminous paint layer formed on the base, and a
scratchable layer formed further on the paint layer, has also drawbacks.
The implement for scratch writing must have a hard point free of ink,
something like a stylus; otherwise the scratched surface would be so
stained that the luminous paint layer might become indiscernible. In
addition, the scratch powder scatters, sometimes seriously marring the
appearance and quality of inscription giving necessary information.
The attempt in EP0700046A2 to overcome these drawbacks is to provide a
luminous or light-storing printed layer on the label base surface or on
the cassette housing, and enable the user to write with a pencil or other
writing implement directly on the printed layer surface. However, the
luminous or light-storing pigment, which consists of a mass of hard and
large inorganic particles, forms such a coarse label surface that the
information written with a pencil is difficult to erase. Ballpoint pens
and fountain pens are of little use on that surface because it repels ink.
Felt-tip pens are useless either, since the tip is easily worn out by the
abrasive action of the coarse pigment particles.
It is already in practice to form a light-storing layer on not only tape
cassette housings but also on other articles by printing with an ink based
on a light-storing pigment (i.e., a light-storing ink) and then print
letters, figures, and patterns in black on the light-storing layer so that
the letters and other inscriptions become visible under luminescent
backgrounds at night or in a dark room. The most important of factors
determining the success of arrangements is the remanent luminescence time
of the light-storing layer. The light-storing paint is required to
maintain a remanent luminescence period of at least 8 hours in which the
letters, figures, and patterns are discernible. In respect of remanent
luminescence, a rule of thumb has hitherto been that the thicker the
light-storing layer the greater the remanent luminescence. It is true that
both the intensity and duration of remanent luminescence increase in
proportion with the thickness of the light-storing layer. However, a too
thick layer requires copious use of the expensive light-storing pigment,
adding to the cost accordingly. It is thus essential that desired
light-storing performance be achieved with as thin a light-storing layer
as possible.
Ordinary light-storing inks use a light-storing pigment mainly of coarse
particles and contain an average of mere 20% or thereabouts of the pigment
(on solids basis), and hence do not possess adequate light-storing
properties.
Moreover, the luminous, light-storing pigments, each consisting of a mass
of hard and large inorganic particles, provide label surfaces rough enough
to mar the appearance. The information written on them with a pencil is
difficult to erase. Ballpoint and fountain pens are difficult to use
because the surfaces repel ink. Felt-tip pens have short life since their
tips are rapidly worn out with abrasion by the coarse pigment particles.
The method of adding a light-storing pigment to the liner sheet base as
taught by Patent Application Kokai No. 63-117383 is not practical. Since
the light-storing pigment is dispersed throughout the resin that
constitutes the base, its concentration is so low that the luminous
intensity is limited and the remanent luminescence period that permits
visual inspection of magnetic tape conditions is as short as about 30
minutes. Even the remanent luminescence makes it hardly possible for the
user to read letters and other indications on the tape cassette housing.
Moreover, because the light-storing pigment generally consists of coarse
particles, a large addition reduces the lubricity characteristics of the
liner sheet. The light-storing capacity cannot be increased, therefore, by
an abundant use of the pigment; hence the light-emitting time that allows
the inspection of tape conditions is limited to only about half an hour.
A further method proposed by EP0700046A2 consists in printing a
light-storing ink layer on an appropriate portion of a tape cassette
housing with an ink containing a light-storing pigment and making the
printed layer surface writable so that the letters and symbols written on
it can be read in the dark too. When the article so coated or printed, for
example, a tape cassette housing, is transparent, the light disperses in
all directions, and merely faint, if any, luminescence results. The
limited light emission attracts but scant attention. A light-storing ink
is translucent in itself (as the binder for the ink must be as clear as
possible to secure ready exposure to light in order to enhance the
light-storing performance). Consequently, a thicker coat of the ink
extends the light-emitting time but does not increase the luminous
intensity accordingly. When a liner sheet surface is printed with an ink
containing a light-storing pigment, an excessively thick coat reduces the
liner sheet functions. Thus the thickness must be restricted to 100 .mu.m
or less, which does not provide sufficient luminous intensity or duration
(at least two hours of light-emitting time being essential) for the user
to look for the tape cassette or make out letters or other inscriptions on
it in the dark.
It is an object of this invention to provide label sheets which overcome
the afore-described drawbacks of the prior art and permit the user to
grasp the inscribed information exactly at night or in the dark, the label
sheets being available at low cost and with excellent writability.
Another object of the invention is to provide light-storing printed
articles having a light-storing layer having a remnant fluorescence for a
long period of time which permits the users to read the characters or
symbols inscribed thereon in a dark place or at night for a long period of
time. Here, the printed articles include articles such as tape cassette,
protective case for such cassette, on which a light-storing layer is
directly printed, and label sheet having a printed light-storing layer
thereon and is adapted to be attached to such articles.
A further object of the present invention is to provide a light-storing
printed article, on which inscription is directly possible or on which is
formed a writable layer which can be writted with a pencil, fountain pen,
ball-point pen, aqueous felt pen.
A further object of the present invention is to provide a stronger
luminescence with a longer period of time than the prior art so as to
allow the users to find the cassettes in a dark place.
SUMMARY OF THE INVENTION
The present invention provides a superior light-storing printed article
such as case for magnetic tape cassette or magnetic disc cartridge,
shutter for magnetic disc cartridge, label sheet suitable to be attached
to any of these articles, each of which has a light-storing layer.
More specifically, the present invention provides a printed article
including an article and a light-storing printed layer on the front side
of said article, said light-storing printed layer containing 50-80 wt % of
light-storing pigment and a balance binder said pigment having D50=22-35
.mu.m and D90=58-80 .mu.m, and the thickness of t he printed layer being
50-150 .mu.m.
Here, Dn (n=50 or 90) is defined as the maximum particle diameter of the
particles amassed from the smallest diameter particles upward until they
account for n %. According to the present invention, fine particles and
coarse particles are appropriately mixed together to enhance the
luminescent efficiency is enhanced by the coarse particles and is improved
by the presence of the fine particles.
Further, according to the present invention, the printed article further
includes a writable printed layer of a transparent or translucent material
formed on the light-storing printed layer.
The above light-storing pigment is generally made of an inorganic material
expressed by the general formula MAl.sub.2 O.sub.4 where M is selected
from Sr, Ca, and Ba) and preferably (Eu, Dy)xSrAl.sub.2 O.sub.4
(x.ltoreq.0.1).
According to the present invention, by appropriately selecting the particle
sizes and the concentration of the light-storing pigments, and the
thickness of the light-storing layer, it has been made possible to produce
light-storing printed articles on which characters and symbols can be
viewed with eyes in a dark place for a long period of time which were not
possible with the conventional light-storing articles, and the
luminescence strength as well as the remnant luminescence have been
improved and the material cost is also suppressed.
One aspect of the present invention relates to a label sheet to be attached
to tape casettes or the like, the label sheet having an adhesive layer and
release paper on the rear side of a label sheet substrate which consists
of a paper or film sheet and also having a light-storing layer printed
with an ink containing a light-storing pigment on the front side of the
substrate.
In this aspect, a printed writable layer printed with a transparent or
translucent writable ink is formed on at least a part of the light-storing
printed layer. This may be used alone or may be applied as a combination
of two types of label sheets.
A further aspect of the invention relates to a light-storing printed
article which includes a light reflective layer formed on an area of a
cassette or an article capable of being seen from outside, and a
light-storing layer containing a light-storing pigment printed on the
reflective layer to increase the luminescence as well as its duration.
There is no particular restriction on the area on which the reflective
layer and then the light-storing layer are formed but the area may be
formed on the surface of a liner sheet of cassette which can be seen
through, or directly on the outer surface of the cassette case.
Alternatively, the reflective layer may be printed on a support film of a
label sheet and then the light-storing layer is printed thereon and this
label sheet is adhesively attached to a desired area on a cassette case.
In either case, a writable layer formed of a translucent or transparent
film may be formed on the light-storing layer. When a light reflective
layer and a light-storing layer are formed directly on a cassette case,
the light-storing layer itself may be made writable or covered with a
writable layer. Label sheet may be similarly constructed so as to make it
writable. When a liner sheet for cassette tape is provided with a
reflective layer and light-storing layer thereon, a writable layer made of
a transparent or translucent film may formed on an area of the cassette
through which the light-storing layer is seen. Thus, the letters, figures
or the like can be readable with the light from the light-storing layer.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a tape cassette to which the present
invention is applicable in common with the prior art;
FIG. 2 is a cross sectional view of a first embodiment of the invention;
FIG. 3 is a cross sectional view of a second embodiment of the invention;
FIG. 4 is a cross sectional view of a third embodiment of the invention;
FIG. 5 is a cross sectional view of a label of the prior art;
FIG. 6(a) is a graph showing the time dependence of light-storing
properties of light-storing printed articles according to the present
invention and a comparative example;
FIG. 6(b) is a graph showing the time dependence of light-storing
properties of light-storing printed articles according to the present
invention and a comparative example;
FIG. 6(c) is a graph showing the time dependence of light-storing
properties of light-storing printed articles according to the present
invention and a comparative example;
FIG. 7 is a schematic view of an apparatus for practicing the method of the
invention;
FIG. 8 is a cross sectional view of the structure of a basic embodiment of
the invention using a reflective layer;
FIG. 9 is a perspective view of an embodiment of the tape cassette
incorporating a reflective layer in accordance with the invention;
FIG. 10 is a cross sectional view of a light-storing label embodying the
invention as using a reflective layer; and
FIG. 11 is an exploded view of another embodiment of the tape cassette of
the invention using a reflective layer.
DETAILED DESCRIPTION OF THE INVENTION
The general belief is that the light-storing properties of a light-storing
printed layer on a label, such as the remanent luminescence and time, are
enhanced in proportion with the thickness of the light-storing printed
layer or the coarseness of the light-storing pigment used. We have found
that the light-storing properties are also largely dependent on the
distribution of particle sizes in the light-storing pigment used. It has
now been found that the control of the particle size distribution in the
pigment to enable it to comprise coarse and fine particles in proper
proportions leads to an increased content of the pigment in the
light-storing ink and that it, in turn, improves the light-storing
properties per unit thickness and thereby makes the light-storing printed
layer thinner than heretofore.
With a light-storing ink, as noted above, the particle size of its
light-storing pigment, the proportion of the pigment in the total amount
(of solids) including the binder, and the thickness of the light-storing
printed layer have material effects upon the remanent luminescence and its
duration. Of these factors, the particle size distribution in the
light-storing pigment is of particular importance.
Light-storing pigments mentioned already are generally used. In particular,
the quality, safety, output, and other considerations make it preferable
to use a product marketed by Nemoto Special Chemical Co. under the trade
designation "N-Yako" (N-Luminescent paint). The product is a material
represented by the formula (Eu,Dy)xSrAl.sub.2 O.sub.4 in which x is 0.1 or
less which is obtained by firing a rare earth element Eu and/or Dy
together with high purity alumina and strontium carbonate at high
temperature of the order of 1300.degree. C. Detailed description is given
in the specification of Patent Application Kokai No. 7-11250 for that
company.
The smaller the particle size the better a light-storing pigment adheres to
other materials. On the other hand, the smaller particles reduce the
light-storing capacity and lessen the remanent luminescence and duration.
This will be confirmed from FIG. 6 to be explained later and from
experiments conducted in connection with the embodiment illustrated.
The proportion by weight of a light-storing pigment to the total amount of
the pigment plus the binder will now be considered. A larger pigment
content naturally makes the remanent luminescence stronger and the
duration longer. When the pigment contains coarse particles, those
particles are accompanied with fine particles that fill up the spaces
among them, thereby increasing the proportion of the pigment. For this
reason the light-storing pigment is desired to have a properly balanced,
broad particle size distribution. Presence of too large particles impairs
screen printability, however. A light-storing pigment with particle size
not exceeding about 100 .mu.m should be used. Since the pigment is used in
mixture with a binder and solvent as an ink for printing to form a
light-storing printed layer, its proportion in the range of 50 to 80% by
weight is appropriate.
A thick light-storing printed layer is desirable because of increased
remanent luminescence and duration, but a thicker layer adds to the cost.
The layer cannot be too thin, on the other hand, because the thickness is
dictated by the size of coarse particles contained in the light-storing
pigment. The thickness of the printed layer usually ranges from 50 to 150
.mu.m.
FIG. 6 indicates, as will be discussed later in Example 1, that the
remanent luminescence and duration are improved by increasing the particle
size and proportion of the light-storing pigment and thereby thickening
the light-storing printed layer. This is because coarse and fine particles
are properly mixed to increase the proportion of the pigment. This is
presumably attributed to the combined effect of the presence of coarse
particles and the increased proportion of the pigment owing to the
intermixture of coarse and fine particles.
The particle size distribution of the light-storing pigment for use in the
present invention is such that, when Dn is defined to be the diameters of
the particles amassed from the smallest diameter particles upward until
they account for n %, D50=22-35 .mu.m and D90=58-80 .mu.m. The maximum
particle diameter is preferably about 100 .mu.m.
Experiments in Example 1 and others show that it desirable that a
light-storing pigment be contained in a proportion of 50 to 80% by weight
to the total amount of the pigment plus the binder, and the thickness of
the resulting printed layer is 50 to 150 .mu.m. The reason for confining
the thickness within that range has already been explained. The use of the
conditions for particle size distribution as defined in the present
invention brings a relatively smooth surface with improved outward
appearance. Although the surface permits direct writing, it is more
advisable to provide an additional clear layer for writing.
For the formation of a light-storing printed layer, the adoption of screen
printing or transfer printing is desirable. Unlike other printing methods,
screen printing applies the ink directly to an object to be printed. The
screen is woven of fibrous lines of metal or resin, and the ink passes
through the openings of the screen onto the surface to be printed. The
method is termed also as stencil printing. A light-storing ink can be used
in the screen printing. An important factor in the printing is the size of
openings, or mesh. A range of 300 to 400 mesh (openings of 30-50 .mu.m
each) is common, but for the practice of the present invention, 120 mesh
or less (openings of 160 .mu.m or more each) is necessary because the
maximum particle diameter of the light-storing pigment is about 100 .mu.m
The optimum mesh is 70 or less (openings of 290 .mu.m or more). The reason
is that a light-storing pigment with a particle size up to 100 .mu.m has a
tendency by nature toward aggregation of about three particles and, even
if it occurs, the aggregates can pass through the openings when the mesh
is 70 or less. In order to change the thickness of the printed layer, it
is advisable to do so by adjusting the angle of and pressure on an
ink-wiping implement known as squeegee. Screen printing comprises
spreading ink on a printing plate with a doctor blade and applying a
pressure on the plate by means of a squeegee. The ink is forced through
the openings onto the surface to be printed, and therefore the squeegee
angle and pressure governs the thickness of the resulting light-storing
printed layer.
The process will be explained below with reference to FIG. 7. There is
shown a screen printing apparatus, with an article 12 to be printed placed
on a table 11 mounted on a housing 10. A printing plate 14 carrying a
screen 13 which has been subjected to image processing as desired is held
above in parallel with the article to be printed. A tilted squeegee 16 is
slidably supported by the underside of a cover 15 which, in turn, is
pivotally supported at one end to be swung open. A proper amount of
light-storing ink is put on the screen 13, the pivotally supported cover
15 is closed, a doctor blade 17 is moved to spread the ink over the entire
surface of the screen, and then the squeegee is moved while applying a
pressure to the plate for printing. The thickness of the light-storing
printed layer can be controlled by adjusting the angle and pressure of the
squeegee. The closer the angle to the vertical with respect to the surface
to be printed the thinner the resulting layer, and the stronger the
pressure the thicker the layer. An intended thickness can be obtained by
properly adjusting the balance between these two conditions.
As for a binder for the light-storing pigment, a material chosen, for
example, from among polyvinyl chloride-acetate, acrylic, urethane, and
epoxy resins, in consideration of its compatibility with the material
constituting the article to be printed, drying property, and other
factors, is mixed with the pigment. The mixture is further mixed with
other necessary additives and diluting solvent to prepare an ink. The ink
is used in printing in a variety of ways. While a solvent type ink has
been described, another type such as ultraviolet (UV) curing type is used
as well.
The transparent or translucent, writable ink that is used in the printed
writable layer may be an ink selected from among inks containing a binder
and a protein powder and inks containing a binder and silica. Such an ink
should be transparent or translucent and should produce a printed layer on
which the user can write anything with a writing implement.
The printed writable layer thus produced is not limited to that for labels.
On a prior art tape cassette shown in FIG. 1, for example, affixing a
label onto a labeling region 2 may be replaced by direct screen printing
to form a light-storing printed layer on the same region. As a further
alternative, the printed layer may be formed on some other part of the
cassette housing or elsewhere, for example, on the plastic shutter on the
window of a floppy disc.
As the printed writable layer, a base (not shown) of a transparent or
translucent film material which does not hamper the excitation of the
pigment in the light-storing printed layer is laminated to the printed
layer. At least the portion of the front side of the base to be made
writable is roughened on the surface by corona treatment or the like to a
surface roughness suited for writing, for example, about 5-30 .mu.m and at
most about 50 .mu.m. If the surface is too smooth it is poorly writable,
but if it is too rough the writing implement wears rapidly and the written
information is difficult to erase. Alternatively, a transparent or
translucent, writable ink, which is either an ink to which 5-20% of a
protein powder binder has been added or an ink prepared by mixing an ink
containing 5-20% of silica as a binder with a light-storing pigment for
the remainder, is used in screen printing to form a light-storing printed
layer.
EXAMPLE 1
Experiments were conducted to assess the effects of particle size
distribution. "N-Yako" of the formula (Eu,Dy)xSrAl.sub.2 O.sub.4 in which
x is 0.1 or less was ground to such a size that the maximum particle
diameter was approximately 100 .mu.m. The ground product was classified to
give a light-storing pigment having a sharply defined distribution of
particles about 30 .mu.m in size on the average (Comparative example).
Also prepared are three specimens; pigments having a broad distribution of
particles having maximum diameter of 100 .mu.m (D50=30 .mu.m, D90=63
.mu.m), (D50=27 .mu.m, D90=75 .mu.m) and (D50=25 .mu.m, D90=35 .mu.m).
Light-storing inks having compositions listed in Table 1 were prepared
from these pigments. Solvent was a mixture of cyclohexanone, ketone,
glycol ester and aromatic hydrocarbon. The inks were applied by screen
printing to bases up to the thicknesses to make light-storing labels. The
labels were irradiated with light of 500 1.times.for 15 minutes that was
necessary for saturation, and the relations between their data of remanent
luminescence and time were found. The results are shown in Table 1 and
FIGS. 8(a), 8(b) and 8(c). Throughout the experiments a combination of
acrylic resin and polyvinyl chloride-acetate was used as a binder.
TABLE 1
__________________________________________________________________________
Comp
Examples
Comp
Examples Comp
Sample 1 2 3 4 5 6 7 8
__________________________________________________________________________
Size .mu.
D50 25 25 27 27 27 27 27 27
D90 35 63 75 75 75 75 75 75
Content wt % 60 60 60 40 50 80 60 60
Thickness .mu. 80 80 80 80 80 80 50 30
Remanent
luminescence hr
0 6 9 9.5 7 8.5 10 8 5
1 4 5 5.5 4.5 5 6 5 3
2 2 3.5 4 2.5 3.5 4.5 3.5 1.5
4 1 2.5 2.5 1.5 2.5 3 2.5 0.5
8 0 1 1 0.5 1 1.5 1 0
__________________________________________________________________________
*Comp = Comparative example
Looking at FIG. 6(a), it is noted that the mixture of various particle
sizes produces a light-storing printed layer having larger remanent
luminescence and longer light-storing time.
Looking at FIG. 6(b), it is noted that the larger the proportion (by
weight) of the light-storing pigment, the larger is the remanent
luminescence and the longer is the light-storing time of the light-storing
printed layer.
Looking at FIG. 6(c), it noted that the thicker the light-storing printed
layer, the larger is the remanent luminescence and the longer is the
light-storing time of the light-storing printed layer.
Consequently, it is concluded that a larger particle size of pigment,
larger contents of pigment and thicker printed layer contribute to larger
remanent luminescence and longer light-storing time. The larger contents
of pigment is materialized by an appropriate concentration of smaller
particles interposed between larger particles. Thus, it is considered that
the effect of coarse particles of the light-storing pigments is combined
with the effect resulting from the coarse particles intermixed with fine
particles.
As a conclusion, the present invention provides a superior light-storing
printed article, which includes a light-storing printed layer comprising
50-80 wt % of light-storing pigment having D50=22-35 .mu.m and D90=58-80
.mu.m based on the total amount of the light-storing pigment and the
binder, and the thickness of the printed layer being 50-150 .mu.m.
EXAMPLE 2
Using the sample 3 in Example 1, a transparent top coat having a
silica-binder mixture shown in Table 2 was applied on the surface of the
light-storing printed layer. The writing ability of the top coat with
various writing instruments, weather test, ink adhesion strength and
surface roughness Ra were measured. The results are shown in Table 2.
TABLE 2
______________________________________
Light-storing
Particle D50 = 27 .mu.m
D50 = 27 .mu.m
ink size D90 = 75 .mu.m D90 = 75 .mu.m
Concentration 60 wt % 60 wt %
Thickness 80 .mu.m 80 .mu.m
Top coat Binder 90 wt % none
Silica 10 wt % none
Writability Pencil acceptable bad
Ball-point pen good poor
Aqueous pen good poor
Oil pen acceptable acceptable
Weather test 70.degree. C. slight change changed
Cycle slight change changed
Ambient temp. no change slight change
Ink adhesion good acceptable
Surface Ra 19.1 .mu.m 38.5 .mu.m
______________________________________
In the light-storing printed layer according to the present invention, as
described above, fine and coarse particles are mixed in proper proportions
so that the coarse particles can bring an increased light emission
efficiency and the fine particles further enhance it. In even more
desirable embodiments the writability of the light-storing printed layers
improved by printing at least a part of the layer surface with a
transparent or translucent, writable ink. Moreover, the resulting layer
has a smooth, good-looking surface which is suited for writing.
Once proper particle size and proportion of a light-storing pigment and
proper thickness of a light-storing printed layer are chosen in conformity
with the present invention, it is possible to manufacture light-storing
printed articles with letters, figures, and patterns on the printed layer
legible during longer light-emitting time than heretofore. Both remanent
luminescence and duration are increased while the material cost of the
light-storing pigment is kept relatively low.
The following are examples of the light-storing printed layer according to
the present invention. They are those applied to label sheets.
More specifically, one aspect relates to a label sheet having an adhesive
layer and release paper on the rear side of a label sheet substrate which
consists of a paper or film sheet and also having a light-storing layer
printed with an ink containing a light-storing pigment on the front side
of the substrate, a printed writable layer printed with a transparent or
translucent writable ink is formed on at least a part of the light-storing
printed layer.
Another aspect is a label sheet having a light-storing printed layer
printed with an ink containing a light-storing pigment on a label sheet
substrate which consists of a transparent or translucent film sheet and
also having an adhesive layer and release paper on the rear side of the
substrate, the light-storing printed layer is provided on the rear side of
the label sheet substrate, the adhesive layer is so provided as to cover
at least a part of the light-storing printed layer, and a printed writable
layer printed with a transparent or translucent writable ink is formed on
at least a part of the front side of the label substrate.
A yet further aspect is a label sheet having an adhesive layer and release
paper on the rear side of a label sheet substrate which consists of a
paper or film sheet and also having a light-storing layer printed with an
ink containing a light-storing pigment on the front side of the substrate,
a transparent or translucent film is laminated to the light-storing
printed layer to cover at least a part thereof and a roughened writable
layer is formed on the film surface.
Another aspect is a label to be affixed to a case or other object sheet
having an adhesive layer and release paper on the rear side of a label
sheet substrate which consists of a paper or film sheet and also having a
light-storing layer printed with an ink containing a light-storing pigment
on the front side of the substrate, the light-storing printed layer is
printed with an ink mixed with a powder pigment which is transparent or
translucent and is writable. The ink may be a protein powder dispersed in
a binder, or silica dispersed in a binder. These inks must be transparent
and writable with writing instruments.
The foregoing described single labels but a composite of first and second
label sheets is also possible. According to this aspect, a first label
sheet having an adhesive layer and release paper on the rear side of a
label sheet substrate which consists of a paper or film sheet and also
having a light-storing layer printed with an ink containing a
light-storing pigment on the front side of the substrate, and a second
label sheet having a transparent or translucent film sheet substrate and
an adhesive layer on the surface of the substrate facing the light-storing
layer of the first label sheet, the film sheet substrate having a writable
layer printed with a transparent or translucent writable ink. In use, the
first and second label sheets are bonded together. With this aspect, the
second label sheet can be removed and exchanged to a new second label
sheet while leaving the first layer as it is.
The printed writable layer may be replaced by a transparent or translucent
sheet having a front surface roughened to a degree to allow writing.
EXAMPLE 3
Referring to FIG. 2, a label sheet is shown as made by first printing the
front side of a base 3 of paper or thin film material with indications for
identification, writable area, and the like by offset or screen printing,
and then a light-storing printed layer 4 is formed on it with the
above-mentioned light-storing ink by screen printing. A printed writable
layer 5 is formed by screen printing, using a transparent or translucent,
writable ink which does not hamper the excitation of the pigment in the
light-storing printed layer, on at least a part of the front side of the
light-storing printed layer 4 which should be rendered writable.
On the rear side of the base 3 is formed an adhesive layer 7, and a sheet
of release paper 9 is attached to the layer. When the label sheet is not
in use, the release paper 9 is weakly affixed to cover the entire surface
of the adhesive layer 7.
EXAMPLE 4
Looking at FIG. 3, there is shown a label sheet whose base 3 is formed of a
transparent or translucent film material which does not interfere with the
passage of light. The rear side of the base 3 is lined with a
light-storing printed layer 4 by screen printing with the light-storing
ink. Further, an adhesive layer 7 for affixing to an area to be labeled is
formed on the light-storing printed layer 4 to cover at least a part of
it. A sheet of release paper 9 is weakly attached to the adhesive layer 7
to cover its entire surface while the sheet is not in use.
The base 3 of film material on which the light-storing printed layer 4 and
adhesive layer 7 have been formed is die cut to slips of given dimensions,
backed with the weakly attached release paper 9. Each die cut slip, or
label, is peeled away from the release paper 9 and glued to a cassette
case housing or the like. Further, a transparent or translucent, printed
writable layer 5 which does not obstruct the excitation of the pigment in
the light-storing printed layer 4 is formed by screen printing on at least
the portion of the front side of the base 3 of transparent film material
that should be made writable.
While single label sheets embodying the invention have thus far been
described, the invention may also be embodied in combinations of two label
sheets as follows.
EXAMPLE 5
Referring now to FIG. 4, a first label sheet is made by printing a base 3
of paper or thin film material with identifiable indications, writable
area, etc. on its front surface by offset or screen printing, and a
light-storing printed layer 4 is formed on it by screen printing using the
above-mentioned light-storing ink. An adhesive layer 7 and release paper 9
are provided on the rear side. A second label sheet consists of a base 3
of transparent or translucent film material formed on the rear side with
an adhesive layer 7 of thin, transparent or translucent film material for
adhesion to the side of the first label sheet where there is the
light-storing printed layer 4, and release paper 9 for temporarily
protecting the adhesive layer. On the opposite or front side of the second
sheet is formed a printed writable layer 5 of transparent or translucent
ink which makes the layer writable. The user writes information on the
second label, peels the release paper from its back side, sticks the label
to the front side of the first label, and then affixes the combined label
to a cassette housing or its case or the like. If the second label is put
on the first, the laminate will function as a light-storing label. This
combination is not only easy to handle but permits effective use of the
valuable light-storing substance through replacement of the second label
on the same first label.
Although the present invention has been described as embodied in label
sheets for use on tape cassette housings and on cases for containing the
cassettes, it is applicable to other uses as well.
The label sheets made by the means described above permit the user to write
easily whatever information needed on the light-storing printed layer,
directly or indirectly, with a free choice of writing implements. The
labels on tape cassette housings and cassette cases are extraordinarily
advantageous in that they render it possible for the user to identify the
needed information exactly at night or in the dark.
EMBODIMENTS HAVING REFLECTIVE LAYER AND LIGHT-STORING LAYER
In FIG. 8, which is a cross sectional view of a basic structure common to
all other embodiments of the invention to be described below, the numeral
22 designates a substrate typified by a specific region of a liner sheet,
base film, or cassette housing. The substrate is a base film in the
embodiment to be described in connection with FIG. 9, and a liner sheet in
the embodiment of FIGS. 10-11.
A reflective layer 23 is formed on the surface of the substrate 22. It
consists of a metallic reflective layer such as a metallic vapor deposited
film or a layer printed with a silver-colored ink containing flaky
aluminum particles. Alternatively, it is a reflective layer formed by
printing with a white ink containing titanium white, calcium carbonate
powder or the like, or some other highly reflective layer.
Over the reflective layer 23 is formed a light-storing ink layer 21.
For example, a white ink is applied to the surface of a clear substrate 22
to form a layer which is 3 .mu.m thick when dry, and then a light-storing
ink is applied onto the white ink layer to a dry thickness of 50 .mu.m.
In the case of a liner sheet, the substrate coated up to this stage is used
as it is. For a label to be affixed or when a label surface is formed by
direct printing, a writable layer 24 as will be explained later in
conjunction with FIG. 10 may be formed on the light-storing ink layer.
Such a writable layer is formed from a transparent resin binder mixed with
protein, starch, or wood cellulose powder. Wood cellulose powder is
obtained, for example, by removing oil and fat from wood, cotton, hemp or
other fiber, boiling the fiber with a dilute alkali solution, drying, and
powdering for ease of inking. Wood cellulose, free of oil or fat, is
excellently hygroscopic (hydrophilic) and provides a highly receptive
surface for writing. More concrete embodiments of the invention will be
described below.
FIG. 9 illustrates a tape cassette 27 in which the invention is embodied.
The invention is applicable to a liner sheet 28 in a cassette housing
having a transparent housing half through which the liner sheet is visible
from the outside. With a tape cassette having a translucent or opaque
housing half, the invention is applicable to its region to be labeled
EXAMPLE 6
FIG. 10 illustrates an example of label to be affixed to the labeling
region 29. As shown, the label is made by forming a reflective layer 23
and a light-storing ink layer 21 formed on the front side of a tape-like
substrate 22 of PET or the like, and a release paper 26 attached through
an adhesive layer 25 to the back side of the substrate 22. When
writability must be imparted, a writable layer 24 is formed over the
light-storing ink layer 21. The structures of the individual layers are
the same as already described. Before use, the label sheet is cut to a
predetermined label size, the release paper 26 is peeled away, and the
back side of the substrate 22 is affixed with the aid of the adhesive
layer 25 to the labeling position 29 of the cassette shown in FIG. 9.
EXAMPLE 7
There is shown in FIG. 11 an embodiment in which the invention is applied
to a liner sheet. Clear housing halves of a tape cassette, a half 32
forming the side A and a half 32 forming the side B, are mated together
along their edges, containing a length of magnetic tape 33 inside. A side
A liner sheet 34 and a side B liner sheet 35 are held, respectively, in
the spaces between the magnetic tape 33 and the housing halves 31, 32 on
the sides A, B. Each of the liner sheets 34, 35 which are transparent is
imparted with lubricity by silicone treatment on the side to contact one
tape edge but is not so treated on the opposite side.
The liner sheets 34, 35 have, respectively, light-storing laminates 38, 39
of the structure shown in FIG. 8, each consisting of a reflective layer 23
and a light-storing ink layer 21, formed in specific positions on the
outer side (facing the inner walls of the housing halves 31, 32 ).
Preferably, in positions on the outer walls of the halves superposing the
light-storing laminates 38, 39, there are attached transparent labels 37,
one for each. Each transparent label 37 may be affixed, with the writable
layer as described above formed on its top. Alternatively, it may be
directly printed with a writable layer. Information such as titles of
music may be written on the transparent label 37.
When the cassette labeled in this way is used, the light, for example, from
the light-storing laminate 38 is reflected on the back side by the
reflective layer 23 and is mostly released toward the outside. For this
reason the luminous intensity in the dark is nearly twice that of the
laminate without a reflective layer and prolonged light emission is made
possible. This not only facilitates the identification of the cassette in
the dark but also enables the user to read letters on the label 37 for an
extended period of time without external light.
In comparative experiments, a white ink for silk screen made by Teikoku Ink
Co. was applied as a white pigment to a liner sheet to form a reflective
layer about 3 .mu.m thick when dry. As a light-storing ink, "N-Yako" of
Nemoto Chemical was applied on the reflective layer to a dry thickness of
about 50 .mu.m. Meanwhile a transparent label 37 of wood cellulose powder
having a particle size of about 5 .mu.m and formed to a layer with epoxy
acrylate and acrylic resin combinedly used as a binder was attached to the
labeling position 36 on the outer wall surface of a cassette half. When
allowed to stand under a fluorescent lamp for 30 minutes, a label 37 not
provided with the reflective layer emitted light sufficient for reading
letters on the label for about 15 minutes, whereas the adequate
light-emitting time of a label having the reflective layer was about 2
hours. The duration for which the light-storing ink layer could simply be
identified was about one hour for the non-reflective label, whereas the
presence of the reflective layer extended the duration to as long as about
6 hours.
Thus, according to the invention, a reflective layer provided behind a
light-storing ink layer improves the luminous intensity and light-emitting
time of the light-storing ink layer, substantially prolonging the time
during which the ink layer and written letters and symbols are
identifiable and legible.
While preferred embodiments have been described, it will be obvious to
those skilled in the art that changes and variations may be made without
departing from the spirit or scope of the invention as hereinafter
claimed.
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